The number of reported sexual assaults in the U.S. armed forces jumped by 50 percent last year, with almost three-quarters of the cases prompting military prosecutions.

Defense Secretary Chuck Hagel said the figures, contained in a 2013 annual report on sexual assault he released Thursday, show that victims have more faith in the system thanks to protections he’s implemented.

“Sexual assault is a clear threat to the lives and the well-being of the women and men who serve our country in uniform,” Hagel told reporters at the Pentagon. “It destroys the bonds of trust and confidence that lie at the heart of our armed forces.”

The Pentagon has been grappling with the problem of military sexual assault for decades, going back at least to the 1991 Tailhook scandal when Navy and Marine Corps aviation officers were alleged to have sexually assaulted 83 women and seven men at a Las Vegas convention.

Hagel has made what on Wednesday he called “this despicable crime” a top priority since becoming Pentagon chief in February 2013. The report showed 5,061 claims of military sexual assault last year, up from 3,374 in 2012. A decade ago, by contrast, there were fewer than 1,700 such claims.

But Nate Galbreath, senior executive adviser in the Pentagon’s Office of Sexual Assault Prevention and Response, said the spike in cases does not actually reflect more instances of assault, just increased reporting of such alleged crimes.

Protect Our Defenders, an advocacy group based in Burlingame, Calif., cast doubt on the Pentagon’s assertion that the number of assaults last year did not actually increase.

“Until the release of DOD’s biannual survey later this year, we will not know the reason for this increase (in reported assaults) _ which could be due to more troops being attacked or a result of the intense public attention to this issue,” said Nancy Parrish, the group’s president.

She said the Pentagon “has released no evidence to prove its claim that victims have more trust in the existing military justice system or the treatment they have received.”

In a surprising statement, Hagel cited “estimates that men comprise more than half the victims of sexual assault in the military.” That claim is at odds with a 2012 Pentagon anonymous survey in which 6 percent of women in uniform said they’d experienced some form of “unwanted sexual contact,” compared with 1.2 percent of men in uniform.

In cases that are prosecuted, the vast majority of victims are women.

Hagel said a far smaller share of male victims than female victims report such attacks. He issued a directive Thursday aimed at persuading more men in uniform who feel they’ve been a target of sexual assault to inform their commanders of the alleged crimes.

“We have to fight the cultural stigmas that discourage reporting (of attacks) and be clear that sexual assault does not occur because a victim is weak, but rather because an offender disregards our values and the law,” Hagel said.

Hagel issued other directives requiring evaluation of commanders’ training on sexual assault, a review of alcohol policies in the military and sustaining a broader military culture in which predatory sexual advances are not tolerated.

Hagel asked his aides to investigate “the risks that alcohol is used as a weapon against victims in a predatory way.” Hagel also issued what he described as “a substantially revised DOD sexual assault prevention strategy,” the first such overhaul since 2008. He said it was compiled in consultation with the Centers for Disease Control and Prevention, the FBI, other law enforcement agencies, colleges and universities.

Sen. Claire McCaskill, a Missouri Democrat, said the increased number of sexual assault victims stepping forward is partially the result of reforms she crafted that became part of last year’s annual defense authorization bill.

“These numbers show concrete progress as our recent sweeping reforms continue to take root and more victims have the confidence in the system to come out of the shadows and report these crimes,” McCaskill, a former sex crimes prosecutor in Kansas City, said in a statement.

Army Maj. Gen. Jeffrey Snow, director of the Pentagon’s sexual assault prevention office, said the Defense Department had created a special counsel program with 185 military attorneys now supporting victims across the armed forces. He said that many sexual assaults in the military are still not reported to superiors, despite last year’s increase in claims.

“While we see indications that our efforts over the last year and a half are having an impact, it does not mean that we are satisfied with our progress,” he said.

In another display of his commitment to the issue, Hagel last week visited a rape crisis organization in Washington, called Rape, Abuse & Incest Network. The Pentagon has contracted with the center, a network of rape crisis groups around the country, to run Safe Helpline, an anonymous hotline launched in 2011.

Hagel said Thursday that while at the center last week, he read notes of gratitude from women who had called the hotline. One of them struck him with special impact.

“It was very simple, very brief,” Hagel said. “It read, ‘Thank you. All you did tonight was save my life.’ That’s pretty powerful.”